The invention discloses a photoelectric chemical sensor for detecting sulfadimethoxine as well as a detection method thereof. The photoelectric chemical sensor comprises an electrode, a WS2 nano-sheetand a DNA aptamer; the WS2 nano-sheet and the DNA aptamer are modified on the surface of the electrode and are tightly contacted. The specificity and the sensitivity of the target compound sulfadimethoxine are detected by utilizing the specificity identification effect of the DNA nucleic acid aptamer and the sulfadimethoxine and performing DNase I catalyzed signal isothermal amplication, and a new method is provided for the fields of environment monitoring, food safety and the like.